The Near-Earth Asteroid (NEA) 2001 FE90 (FE90), discovered by B. Skiff during
the LONEOS survey, was identified as a Potentially Hazardous Asteroid by the
Minor Planet Center. A perigee of 0.018 AU occurred on 2009 June 28.38, near
which time FE90 was scheduled to be imaged by the JPL Planetary Radar Team. Our
optical observations revealed a
small, monolithic, and fast-rotating [P_syn = 28.66+/-0.06 min] NEA. We conclude
that FE90 is likely an shard arising from the disruption of a well-differentiated
parent body. Southern hemisphere observers are encouraged to collect
light-curves of FE90 to facilitate shape/spin modeling. FE90 will remain at
declinations near -40 deg and brighter than m_V ~ 19 from early July through
mid-August.

Optical spectroscopy was obtained at the Palomar 5-m
telescope on the night of June 19.2, see
Figure 1.
A comparison with ~1300 asteroid spectra in the SMASS II database (Bus
& Binzel 2002) found FE90 best matched by the A-type asteroid 289 Nenetta.
A-type asteroids are olivine-rich and are thought be the product of partial/full
melting of a large parent body (Reddy et al. 2005). Our spectrum was
acquired at substantial solar phase angle and until we can
quantify the effects of phase reddening, we consider our taxonomic classification tentative.

R-band photometry of FE90 was obtained at the JPL Table Mountain 0.6-m
telescope (TMO) over 5 nights from 06/20 to 07/01, see Table 1.
Each night's data was analyzed via standard Fourier techniques,
as shown in Figures 2 though 6
[2][3][4][5][6].
The light-curve amplitudes were consistent with a minimum 2:1 axial
ratio. The rapid rotation of FE90 implies a monolithic body, a density of over
40 gm per cm^3 is required to maintain integrity if strength-free. Two solar
phase curves are given in
Figure 7,
derived using light-curve subtracted measurements (red symbols) and data
restricted to near the maximum brightness peaks of the individual light-curves
(green symbols). The Maximum Brightness method minimizes the effects of
non-spherical shape (Harris & Lupishko 1989). The
G values were consistent with a moderate-to-high albedo asteroid. With
H_oR = 20.11 mag and the V-R color given in Figure 1, the effective diameter of
FE90 is likely near 200 m, assuming an albedo of 0.25.

The research descripbed in this telegram was carried out at the
Jet Propulsion Laboratory, under contract with the National
Aeronautics and Space Administration.